As insulating covering materials of cables used in automobiles, robots, electronic machinery and tools, and the like, thermoplastic polyurethane resin compositions having good mechanical properties and flexibility are employed. In many cases, after the thermoplastic polyurethane resin compositions are molded, they are irradiated with ionizing radiation to effect crosslinking, in order to improve heat resistance, chemical resistance, and water resistance.
When such a cable is connected to an electrode terminal or a part of machinery and tools, such as a sensor, the connected section and the nearby part around it are protected in an airtight manner or watertight manner by molding with a mold resin (a molded body).
In order to secure the airtightness or watertightness with a mold resin in this way, PBT resins and PA resins are often used as molding materials, since they are readily molded and have excellent mechanical strength.
However, depending on the choice of the covering material on the cable and the molding material, the difference in heat shrinkage factor between the materials causes the problem that the heating and cooling processes at the time of end working or during use bring about a gap at the interface between the cable and the molded body, and water penetrates through the gap formed at the interface. When water penetrates through the gap formed at the interface, the conductors of the cable are corroded and malfunctions, including deterioration of the performance of the connected part of machinery and tools, occur. Therefore, various sealing measures for securing airtightness and watertightness are needed. As a result, the operation at the time of end working becomes extremely complicated, and thus the operation requires a high degree of skill.
To solve such a problem, it is conceivable that, taking the adhesion between the covering material of the cable and the molding material into account, the covering material may be made of a material that is the same as or similar to the molding material, but these resin materials have poor formability and workability as a covering material of cables, and they have a problem in the flexibility thereof that is required for electric wires. Further, even in the case of covering materials whose adhesion to molding materials is satisfactory as an initial property, if the materials fail in airtightness or watertightness in a heat shock test or show deterioration of the properties in a water resistance test, they are not practical for long-term usage.